Abstract A major concern in cochlear implantation is the loss of residual hearing associated with surgery. Hence, many candidates are faced with the decision to relinquish their remaining acoustic hearing in exchange for electric hearing via the cochlear implant (CI). A potential solution is a stimulation strategy termed Electric acoustic stimulation (EAS), which has been used to describe the ipsilateral combination of electric hearing via a CI and acoustic hearing via a hearing aid. This, however, requires preservation of residual hearing, which has been possible but inconsistent. A new technology to potentially improve hearing preservation, intraoperative electrocochleography (ECochG), has been introduced and it was recently implemented into commercially available CI systems. Studies comparing EAS with conventional CI have were able to demonstrate a performance benefit of EAS. However, these studies have compared conventional CI candidates to EAS candidates with more residual hearing. Thus, the clinical importance of residual acoustic hearing in cochlear implantation (CI) remains unclear. Therefore, the present protocol seeks to answer two critical clinical questions in cochlear implantation: (Specific Aim 1) Are cochlear implant electrode insertions using Electrocochleography (ECochG) feedback better for achieving hearing preservation (HP) and (Specific Aim 2) is combined ipsilateral EAS better than non-HP (conventional) cochlear implantation among CI candidates with substantial residual hearing (EAS candidates). We plan to enroll and randomize EAS candidates in seven large US centers. Patients will be assigned to either intraoperative ECochG monitoring or conventional CI electrode insertions. Hearing preservation and other performance outcomes will be recorded and analyzed between the groups to assess the clinical value of intraoperative monitoring. Further, subjects from both groups will have either useable or no useable residual hearing as the result of surgery. Audiometric and patient reported performance outcomes will be obtained and evaluated for 24 months following initial stimulation. In summary, the present proposal aims to answer two critical clinical questions: Is CI electrode insertion based on ECochG better for achieving HP? and Is EAS better than conventional cochlear implantation among EAS candidates? A positive answer to these questions will inform an evidence-based clinical practice for EAS candidates that uses longer electrodes, broadens the candidate pool by including patients with greater levels of residual hearing, and potentially improves outcomes following CI.